There has been a demand for portable devices such as a mobile telephone having smaller size, and displays for the devices should be reduced in size as well. This is why light emitting type displays such as organic EL devices that can be thinned have come to be used more than conventional LCDs that have been used for the displays.
The display for a mobile telephone has a part indicating the state of the telephone such as the remaining talk time and the field intensity. This state indicating part shows fixed patterns and therefore has its characteristics such as luminance more degraded than the other part, which results in so-called “image burn.” In order to solve this problem, non-inverted display and inverted display may regularly be switched, but such switching occurring in the use of the device might not only irritate the user, but also could be mistaken as the sign of a failure.
When a light emitting display device is used for the display of a mobile telephone and inverted display is carried out, the power consumption increases, and the usable time without charging is shortened.
The present invention is directed to a solution to the above problems, and it is an object of the invention to prolong the useful life of a display device without letting the user of the device conscious of changes in the display state of the display device. Another object of the invention is to prevent the power consumption from increasing, and the usable time without charging from being shortened even when a light emitting display device is used.